In recent years, a portable electronic apparatus has remarkable progress for becoming multifunctional and advanced functionality. A mobile phone will be considered as an example. Each mobile phone manufacturer has developed the mobile phone with not only a native function as telephone but also a plurality of advanced functions under a situation that the number of mobile phone owners is increasing rapidly. As a result, the mobile phone gets to have enhanced convenience.
The functions equipped in the mobile phones, for example, are a digital camera function with megapixels, a navigation function using GPS (Global Positioning System) and a television (TV) function which receives TV broadcasting including digital broadcasting.
By using the TV function that a mobile phone has, when a user is watching TV broadcasting, the user may switch a channel to other channels. At this time, in a case of digital broadcasting, the mobile phone executes a synchronizing processing in a tuner, a processing which interprets a program information, a waiting processing for data or the like before changing to the other channels. Hence, the mobile phone cannot smoothly switch the channel in digital broadcasting compared with a case of analog broadcasting.
In a digital broadcasting system, it is general to multiplex a coded video and a coded sound with a multiplexing format and deliver that multiplexed data. As a method of coding video, for example, there are MPEG (Moving Picture Experts Group)-2 video and H.264/AVC (Advanced Video Coding). As a method of coding sound, for example, there are MPEG (Moving Picture Experts Group)-1 audio and AAC (Advanced Audio Coding). As the multiplexing format, for example, there is MPEG-2 transport stream.
In an IPTV (Internet Protocol TeleVision) system, it becomes general to deliver a data multiplexed with the MPEG-2 transport stream by IP (Internet Protocol) protocol similarly to the above mentioned.
When the above-mentioned data is received, the mobile phone establishes synchronization for a physical layer (such as a TV tuner in the case of TV broadcasting), at first. The mobile phone interprets a stream configuration based on a broadcast stream (such as the MPEG-2 transport stream) obtained after establishing the synchronization for the physical layer. Based on this interpretation, the mobile phone separates a video signal and a sound signal, and executes a decoding processing. At this time, the mobile phone extracts a broadcast reference clock (PCR (Program Clock Reference) in the case of MPEG-2 transport stream) from the stream. Next, the mobile phone generates a clock (STC (System Time Clock)), which is synchronizing with a broadcast wave, inside the receiver. Finally, in conformity with System Time Clock, the mobile phone transmits the decoded video and the decoded sound data to a display and a speaker based on a time-stamp to which the decoded video and sound data are respectively attached. As a result, the display of the mobile phone begins to display a video of the selected channel, and the speaker of the mobile phone begins to output a sound of the selected channel. And then, the user can begin to watch the stream after the cannel selection.
The successive operations (that is, the processing which establishes the synchronization for the physical layer, the processing which interprets the stream configuration, the processing which separates each data, the processing which decodes each data and the synchronization processing which utilizes the time-stamp) take time respectively. For example, in a case of One Seg (One Segment broadcasting, Partial reception service of one segment for mobile phone and mobile terminal) in Japan, it generally takes longer than four seconds so that the mobile phone displays the video based on the successive operations after a user selects. In other words, a user is barely able to watch the video of the selected channel after passing longer than four seconds from the channel selection.
As technology for reducing a waiting time on the channel changing, for example, there is a technology disclosed in a patent document 1. In the technology disclosed by the patent document 1, a demodulated data regarding all channels is stored in a buffer for each channel. And when the channel is changed, the demodulated data is read from the buffer.